CODEWITHSUNDEEP
python-3.xkivykivy-language
RafaCRz
RafaCRz

Reputation: 67

How to use on_enter event to change screens on kivy?

So, here is what I'm trying to do: when entering on the first screen of my app, I want it to check if some files exist in given directory. If they exist, I want it to immediately change to another screen.

I've tried the following:

main.py

from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from os import listdir

class Manager(ScreenManager):
    pass

class CreateFileScreen(Screen):

    def on_enter(self):
        try:
            files = listdir("data/files")
            if "file.dat" in files:
                self.parent.current = "login"
            else:
                pass
        except FileNotFoundError:
            pass

class LoginScreen(Screen):
    pass

class ExampleApp(App):

    def build(self):
        return Manager()

if __name__ == "__main__":
    ExampleApp().run()

example.kv

#:kivy 1.10.0

<CreateFileScreen>:
    BoxLayout:
        Label:
            text: "This is Create File Screen"
            font_size: "30sp"

<LoginScreen>:
    BoxLayout:
        Label:
            text: "This is Login Screen"
            font_size: "30sp"

<Manager>:

    CreateFileScreen:
        name: "createfile"
    LoginScreen:
        name: "login"

When file.dat does exist in data/files I get the following error: kivy.uix.screenmanager.ScreenManagerException: No Screen with name "login".

Any idea on how to fix this?

Upvotes: 5

Views: 8204

Answers (1)

el3ien
el3ien

Reputation: 5405

The problem is that on_enter is executed before the screen gets its name.
You can make a change_screen method, then call it with Clock.schedule_once. That way it will be called the next frame. 

from kivy.clock import Clock

class CreateFileScreen(Screen):

    def on_enter(self):
        Clock.schedule_once(self.change_screen)

    def change_screen(self, dt):
        try:
            files = listdir("data/files")
            if "file.dat" in files:
                self.manager.current = "login"
            else:
                pass
        except Exception as e:
            print(e)

Upvotes: 8

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